Posted in | Quantum Physics

Quantum Fluids May Mix in Very Weird Ways

New computer simulations of exotic states of matter, called Bose-Einstein condensates (BECs), have revealed that quantum fluids might mix in really strange ways.

Sort of looks like a frog, right? Researchers at The Ohio State University and their colleagues are using a supercomputer to simulate what happens when two exotic superfluids mix. The simulations have produced some unusual shapes, including “mushrooms” and this frog-like shape. (Image credit: Kui-Tian Xi, courtesy of The Ohio State University) (K.-T. Xi et al., Phys. Rev. A (2018))

In the far future, BECs might power up innovative types of ultra-fast computers. However, currently, researchers are just attempting to get insights into the basic physics related to the behavior of BECs.

This is precisely the study conducted by Kui-Tian Xi, an Ohio State University visiting scholar in the Department of Physics, and his colleagues when they used a supercomputer to simulate the outcomes of mixing two magnetically polarized BECs.

Images of the simulations, reported in the Physical Review A journal, look like ink blot tests that can be deciphered in an unlimited number of ways. When one fluid percolated up through the other, Xi initially observed the blobs forming a turtle (i.e., a pattern with six finger-like shapes that resembled a head, tail, and four legs, like a turtle), then a frog (back legs akimbo), and lastly, an explosion of mushroom shapes.

Although this was not what Xi precisely expected, he was not very astonished, either.

To be honest, I did expect that I may see some interesting dynamical properties. But when I first saw the turtle, I thought I might have calculated the parameters of the simulation wrong,” he stated. “Then I realized there might be some kind of instability at the interface of the fluids, just like those of classical fluids.”

BECs are gases formed of atoms so cold that their entire movement is nearly stopped. As predicted by the Indian physicist Satyendra Nath Bose and Albert Einstein in the 1920s—and experiments were eventually demonstrated in the 1990s—BECs exhibit weird characteristics since all the atoms are filled into the same quantum state.

BECs are superfluids by their very nature. They are assumed to be frictionless and hence should collectively flow with zero viscosity. However, the parameters of the simulation (for example, the strength of the magnetic interactions) were adjusted by Xi, the two fluids mixed as though one was more viscous when compared to the other—similar to the manner in which viscous hot wax bobs through water, which is less viscous, inside a lava lamp.

Xi and his team, including Hiroki Saito, study leader and professor of engineering science at the University of Electro-Communications in Japan, consider that the simulations provide clues to various phenomena observed by physicists in real-time experiments. In some special cases, BECs do appear to act like normal matter.

Specifically, Xi notifies recent numerical simulations carried out at Newcastle University, in which liquid helium, another superfluid, formed waves of turbulence when it was made to flow over the rough surface of a wire.

Although the reason behind the weird simulated BEC behavior is yet to be known, Xi stated that prevalent technology would enable experimental physicists to perform the experiment in real time. However, being a theorist, his focus will be on the probable implications of a growing link between the behaviors of classical and quantum fluids.

The study was co-authored by Xi and Saito in collaboration with Tim Byrnes from the New York University Shanghai. The Japan Society for the Promotion of Science mainly funded the study. The simulations were performed on the Prince computer cluster at New York University.

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